Experimental investigation of right-left flow balance concepts for a total artificial heart.

A total artificial heart (TAH) must be designed to autonomously balance the flows of the systemic and pulmonary circulation to prevent potentially lethal lung damage. The flow difference between the systemic and pulmonary circulation is mainly caused by the bronchial (arteries) shunt flow and can change dynamically. The ReinHeart TAH consists of only one actuator that ejects blood alternately from the right and left pump chamber. This design entails a coupling of the right and left stroke and thus, complicates the independent adaptation of the right and left flow. In this experimental study on the ReinHeart TAH, four concepts to keep the flows well balanced were investigated using an active mock circulation loop for data acquisition. Three concepts are based on mechanical design changes (variation of pusher plate shape, flexible right pump chamber housing, and reduced right stroke volume) to achieve a static flow difference. In combination with these static concepts, a concept influencing the ratio of systole and diastole duration to respond to dynamic changes was studied. In total, four measurement series, each with 270 operating points, to investigate the influence of circulatory filling volume, heart rate, bronchial shunt flow, and lung resistance were recorded. In the course of this study, we introduce a concept deviation indicator, providing information about the efficiency of the concepts to balance the flows based on changes in lung's blood pressures. Furthermore, the distribution of the measured data was evaluated based on bubble plot visualizations. The investigated variation of the right pusher plate shape results in high lung pressures which will cause lethal lung damage. In comparison, a flexible right pump chamber housing shows lower lung pressures, but it still has the potential to damage the lungs. Reducing the stroke volume of the right pump chamber results in proper lung pressures. The flow balance can dynamically be influenced with a positive effect on the lung pressures by choosing a suitable systole-diastole-ratio. The results of this study suggest that an adequate right-left flow balance can be achieved by combining the mechanical concept of a reduced right stroke volume with an active control of the systole-diastole-ratio.

Estimation of Filling and Afterload Conditions by Pump Intrinsic Parameters in a Pulsatile Total Artificial Heart.

A physiological control algorithm is being developed to ensure an optimal physiological interaction between the ReinHeart total artificial heart (TAH) and the circulatory system. A key factor for that is the long-term, accurate determination of the hemodynamic state of the cardiovascular system. This study presents a method to determine estimation models for predicting hemodynamic parameters (pump chamber filling and afterload) from both left and right cardiovascular circulations. The estimation models are based on linear regression models that correlate filling and afterload values with pump intrinsic parameters derived from measured values of motor current and piston position. Predictions for filling lie in average within 5% from actual values, predictions for systemic afterload (AoPmean , AoPsys ) and mean pulmonary afterload (PAPmean ) lie in average within 9% from actual values. Predictions for systolic pulmonary afterload (PAPsys ) present an average deviation of 14%. The estimation models show satisfactory prediction and confidence intervals and are thus suitable to estimate hemodynamic parameters. This method and derived estimation models are a valuable alternative to implanted sensors and are an essential step for the development of a physiological control algorithm for a fully implantable TAH.

Effects of biventricular shunt on pump characteristics in a maglev total artificial heart.

Severe left ventricular failure can progress to right ventricular failure, necessitating alternatives to heart transplantation, such as total artificial heart (TAH) treatment. Conventional TAHs encounter challenges associated with miniaturization and hemocompatibility owing to their reliance on mechanical valves and bearings. A magnetically levitated TAH (IB-Heart) was developed, utilizing a magnetic bearing. The IB-Heart features a distinctive biventricular shunt channel situated between the flow paths of the left and right centrifugal blood pumps, simplifying and miniaturizing its control system. However, the impact of these shunt channels remains underexplored. This study aimed to investigate the effects of shunt flow on pump characteristics and assess the IB-Heart's potential to regulate flow balance between systemic and pulmonary circulation. At a rotational speed of 2000 rpm and flow rate range of 0-10 L/min, shunt flow exhibited a minor impact, with a 1.4 mmHg (1.3%) effect on pump characteristics. Shunt flow variation of about 0.13 L/min correlated with a 10 mmHg pressure difference between the pumps' afterload and preload conditions. This variance was linked to changes in the inlet flow rates of the left and right pumps, signifying the ventricular shunt structure's capacity to mirror the function of an atrial shunt in alleviating pulmonary congestion. The IB-Heart's ventricular shunt structure enables passive regulation of left-right flow balance. The findings establish a fundamental technical groundwork for the development of IB-Hearts and TAHs with similar shunt structures. The innovative coupling of centrifugal pumps and the resultant effects on flow dynamics contribute to the advancement of TAH technology.

Research on Modeling and Simulation of Fuel Cell Bus Power System Based on Forward-Backward energy flow balance method.

The modeling and simulation research of fuel cell buses' power system is an important part of accelerating the process of industrialization. This paper firstly analyzes the advantages and disadvantages of different topologies of power systems to determine the optimal configuration, then conducts the parameter matching study of the power system, derives and determines the main vehicle dynamics parameters and the total power demand of the power system, and further completes the parameter matching of the drive motor, gear ratio and power supply, as well as the design of the fuel cell stack. On the Matlab/Simulink platform, the forward-backward energy flow balance method is used to establish a fuel cell power system model divided into power calculation modules and power shunt modules. Finally, model simulation and comparative analysis was car-ried out. The simulation results of the power system model in this paper were compared with the data of the 2010 World Expo FCB real-vehicle test. The result shows that the simulation results of the dynamic system is in good agreement with the real vehicle data. The power system model conforms to the actual situation, has feasibility and high engineering value.

Flow balance optimization and fluid removal accuracy with the Quanta SC+ hemodialysis system.

BACKGROUND: Fluid management is integral to hemodialysis, both to correct abnormalities in a patient's plasma composition and to maintain fluid balance. Consequently, accurate net fluid removal during treatment is a critical design element of hemodialysis machines. As dialyzers have evolved, with increased ranges of ultrafiltration coefficients available, it has become more challenging for dialysis machines to minimize errors in flow balance and net fluid removal. RESEARCH DESIGN AND METHODS: This paper describes the design, evaluation and experimental performance of the flow balance and ultrafiltration module of the SC+ system to deliver clinically specified fluid removal with both passive and active control measures, in laboratory conditions designed to simulate a wide range of therapies. RESULTS: The use of passive and active control allows the errors to be minimized across a wider dynamic range of conditions. For the SC+ system, the average flow balance error was 1 mL/hr with an SD of 19 mL/hr and with ultrafiltration it was 13 mL/hr and an SD of 20 ml/hr across all conditions. CONCLUSIONS: This paper demonstrates that the SC+ hemodialysis system, a small, simple and versatile CE marked device, operates within the limits required by international standards across a wide range of experimental conditions.